1. Field of the Invention
The present invention relates to a touch panel and particularly to a device and method for determining a touch position on a sensing area of a capacitive touch panel.
2. Description of the Related Art
Conventionally, an electronic device is inputted by a mouse and a keyboard, which is yet not intuitive to human. Thereafter, touch panel has been developed and gradually widely used in various large and small sized electronic devices. In inputting to the electronic device by using the touch panel, a user touches on the touch panel by his finger or a stylus, and a sensing means lying under the touch panel then detects a position of the touch on the touch panel. The information of the detected position is subsequently transmitted to a circuitry unit cooperating with a central processing unit (CPU) for obtaining an electric signal representing this information and then interpreting the information to obtain a position signal for the touch position to achieve a desired function. There have been several kinds of touch panel in terms of the sensing means or mechanism so far: resistive, capacitive, surface acoustic wave (SAW), infrared (IR) type touch panels, etc.
In the capacitive touch panel, a capacitive mechanism is used for position determination where several currents are supplied onto the touch panel when a touch is impinged on the touch panel and are measured and then a relationship among the measured currents is deduced to obtain the touch position. Referring to FIG. 1, specifically, the capacitive touch panel 10 comprises a sensing area 11 logically comprising regions A, B, C and D having together the arrangement as shown. The regions A, B, C and D are alternatively applied with identical alternating current (AC) scan signals AC1, AC2, AC3 and AC4, respectively. When a touch point P is registered with the sensing area 11 of the touch panel 10, currents I1, I2, I3 and I4 provided by the scan signals AC1, AC2, AC3 and AC4, respectively, to the touch panel 10 are measured and the measured currents I1, I2, I3 and I4 can be calculated to obtain an abscissa and an ordinate values (X, Y) of the touch point P. The currents I1, I2, I3 and I4 vary since the touch point, e.g. a fingertip of a user, P is electrically conductive and thus changes the resistance of the touch point P on the sensing area 11. Specifically, the coordinate (X, Y) of the touch point P is determined by the following equation:
                              X          =                                                    (                                                      Δ                    ⁢                                                                                  ⁢                    I                    ⁢                                                                                  ⁢                    4                                    +                                      Δ                    ⁢                                                                                  ⁢                    I                    ⁢                                                                                  ⁢                    3                                                  )                            -                              (                                                      Δ                    ⁢                                                                                  ⁢                    I                    ⁢                                                                                  ⁢                    1                                    +                                      Δ                    ⁢                                                                                  ⁢                    I                    ⁢                                                                                  ⁢                    2                                                  )                                                                    ∑                i                            ⁢                              Δ                ⁢                                                                  ⁢                Ii                                                    ,                            (        1        )                                and                                                                      Y          =                                                    (                                                      Δ                    ⁢                                                                                  ⁢                    I                    ⁢                                                                                  ⁢                    1                                    +                                      Δ                    ⁢                                                                                  ⁢                    I                    ⁢                                                                                  ⁢                    4                                                  )                            -                              (                                                      Δ                    ⁢                                                                                  ⁢                    I                    ⁢                                                                                  ⁢                    2                                    +                                      Δ                    ⁢                                                                                  ⁢                    I                    ⁢                                                                                  ⁢                    3                                                  )                                                                    ∑                i                            ⁢                              Δ                ⁢                                                                  ⁢                Ii                                                    ,                            (        2        )            wherein ΔIi is a difference of each of the currents Ii (i=1, 2, 3 and 4) before and after the touch point P is registered with the sensing area 11 of the touch panel 10.
However, since the touch panel 10 and a user generally correspond to different reference potentials, the touch panel 10 is susceptible to noise brought by the user's fingertip and even the environment surrounding the touch panel 10, for example, electromagnetic radiation of a liquid crystal device (LCD) or cathode ray tube (CRT). As a result, the thus detected touch position on the touch panel 10 is generally accompanied with an error.
In this regard, many noise elimination technologies have been set forth. The present invention also sets forth herein a device and method for determining a touch position on a capacitive touch panel.